The invention relates to the field of organic synthesis. Particularly, the invention relates to the rearrangement of epoxides as well as the preparation of allylic alcohols and alpha,beta-unsaturated carbonyl compounds, which find a wide spectrum of application in many areas of synthetic and industrial organic chemistry.
Allylic alcohols are widely used in the chemical industry, for example, as flavor and fragrance ingredients. Moreover they can serve as intermediates, e.g., in the manufacture of alpha, beta-unsaturated carbonyl compounds by Oppenauer oxidation.
In general, the rearrangement of epoxides to allylic alcohols and further oxidation of obtained alcohols can be expressed as follows: 
where R1-R3 represent hydrogen atom, alkyl, aryl, aralkyl groups, or together form a cycloalkyl group.
Traditional methods used for the rearrangement of epoxides to allylic alcohols include:
A. Stoichiometric Opening of the Epoxide Ring with Strong Bases:
See J. K. Crandall and M. Apparu, xe2x80x9cBase-promoted Isomerizations of Epoxidesxe2x80x9d in: Organic reactions, John Wiley and Sons, Inc., New York, Chichester, Brisbane, Toronto, Singapore, 1983, Vol. 29, pp. 345-443 which is incorporated by reference in its entirety.
This method suffers from a number of disadvantages. For example, the use of at least stoichiometric amount or, in most reactions, a large excess of the expensive reagent (lithium amide, lithium diisopropylamide, butyl lithium, aluminum amides, potassium butoxide, etc.) is a major disadvantage of this method. In addition, when the epoxide ring opening may proceed in different directions, this method lacks the selectivity and flexibility to lead the process towards formation of a specific product. 
It is generally accepted that proton abstraction in the rearrangement of epoxides to allylic alcohols occurs at the least substituted carbon (J. Gorzynsky Smith, Synthetically useful reactions of epoxides, Synthesis, 1984, (8), pp. 629-656, which is incorporated by reference in its entirety).
According to this rule in the rearrangement of 1,2-limonene oxide (1, see scheme 1) promoted by strong bases a preferential formation of iso-carveol (3) occurs (Y. Bessiere and R. Derguini-Boumechal, J. Chem. Res. (S), 1977, (12), pp. 304-305). The highest selectivity to carveol (2), which is a flavor component and an intermediate in synthesis of carvone (7), was 22%.
B. Homogeneous Catalytic Rearrangement of Epoxides in the Presence of Metal Alkoxides.
The most widely used catalysts in this group are aluminum isopropoxide (E. H. Eschinasi, Isr. J. Chem., 1968, 6, pp. 713-721), titanium alkoxides (JP 50/58031, English translation of the full text), and zirconium butoxide (U.S. Pat. No. 4,496,776), all of which are incorporated by reference in their entirety.
In the presence of these catalysts the selectivity of 1,2-limonene oxide rearrangement to carveol is between 24% (aluminum isopropoxide) and 60% (titanium isobutoxide). Common disadvantages of these catalysts are complicated work-up of the reaction mixtures, and low activity and selectivity, which limits their applications.
C. Heterogeneous Catalytic Rearrangement.
Numerous heterogeneous catalysts have been suggested for the conversion of epoxide to allylic alcohols. They include:
a) Metal oxides, specifically different grades of alumina, silica, titania, zirconia and mixed oxides (see review by K. Tanabe, R. Ohnishi, K. Arata, xe2x80x9cRearrangement of epoxides over solid acid and base catalystsxe2x80x9d, chapter 2.5 in: Terpene Chemistry, ed. J. Varghese. Tata McGraw-Hill Publishing Company, Ltd., 1982, pp. 67-88, and references therein, each of which are incorporated by reference). The highest selectivity achieved in 1,2-limonene oxide rearrangement to carveol catalyzed by metal oxides was 59% over aluminum oxide (K. Arata, K. Tanabe, Chem. Letters, 1976, pp. 321-322 which is incorporated by reference).
b) Metal phosphates. Commercial method for production of allyl alcohol is based on propylene oxide rearrangement in the presence of lithium phosphate (U.S. Pat. No. 2,426,624 and U. S. Pat. No. 2,986,585 which are incorporated by reference). The process is carried out at 275-300xc2x0 C. The selectivity of allyl alcohol formation is about 80%. Lithium phosphate supported on silica (U.S. Pat. No. 5,455,215) and sodium phosphate supported on zirconia (JP 11/49709) were also used to effect the rearrangement of epoxides. Rearrangement of 1,2-limonene oxide in the presence of lithium phosphate was studied by S. G. Traynor et al. (Proceedings of The VIII International Congress of Essential Oils. Fedarom, Grasse, 1980, pp. 591-594). The reaction was very slow. The selectivity of trans-1,2-limonene oxide transformation to cis-carveol was 18.1% at 66.2% conversion (57 hours, 200xc2x0 C.).
The selectivity of cis-1,2-limonene oxide transformation to trans-carveol was 13.6% at 69.9% conversion (57 hours, 200xc2x0 C.). In this reaction a significant amount of carbonyl compoundsxe2x80x94aldehyde (6) and ketone (4)xe2x80x94was produced (10.9% and 4.3% respectively). The major product was iso-carveol (3)xe2x80x9468.7% in case of cis-1,2-limonene oxide rearrangement and 59.9% in case of trans-1,2-limonene oxide rearrangement. Each of the above-discussed documents are incorporated by reference in their entirety.
As can be seen, traditional methods for epoxide rearrangement to allylic alcohols fail to selectively produce carveol from 1,2-limonene oxide.
It was reported that in some cases preparation of allylic alcohols from epoxides is accompanied by formation of a significant amount of the corresponding unsaturated carbonyl compound.
For example, in the rearrangement of 1,2-limonene oxide over metal oxides and binary oxides, the selectivity of carvone (7) formation was as high as 35% at 75% conversion of epoxide. However, total selectivity to carveol and carvone was only 59% (J. Jayasree, Ind. J. Chem., 1997, Vol. 36A, (9), pp. 765-768). Formation of unsaturated carbonyl compounds during the rearrangement of epoxides results from the Oppenauer oxidation of the allylic alcohol. This reaction is possible because (i) some epoxide rearrangement catalysts are also capable of catalyzing the Oppenauer oxidation; and (ii) by-products of the rearrangementxe2x80x94dihydrocarvone (4) and aldehyde (6) in the discussed examplexe2x80x94can act as hydrogen acceptors. It is clear that the more alpha,beta-unsaturated compound is produced, the lower is total yield of allylic alcohol and alpha,beta-unsaturated carbonyl compound, since more epoxide undergoes undesired transformation to the corresponding carbonyl compounds (4 or 6) and further to saturated alcohols (8) or (9). The sequence of the epoxide rearrangement and the Oppenauer oxidation of allylic alcohol utilizing carbonyl by-products as hydrogen acceptors is presented in scheme 2. 
In many instances preparation of alpha, beta-unsaturated carbonyl compounds from epoxides by the sequence of rearrangement and oxidation reactions is an ultimate goal. Yet, none of the traditional techniques is capable of combining these two steps to produce high yields of alpha, beta-unsaturated carbonyl compound, particularly in a one-pot process.
The present invention is based in part on the discovery that the inclusion of certain activator/modifier(s) in a catalyst system can significantly improve the activity and/or selectivity of the catalyst system, particularly in connection with the rearrangement of epoxides. For example, it has now been found that variety of allylic alcohols can be selectively produced by rearrangement of corresponding epoxides in the presence of the catalyst system that comprises primary catalyst and activator/modifier.
Among other aspects, the present invention includes a catalyst system that can be used to achieve:
a) preparation of allylic alcohols by rearrangement of the corresponding epoxide, when the allylic alcohol is a desired product;
b) subsequent reaction, e.g., selective oxidation, of the allylic alcohols obtained in step (a) to afford a desired product, e.g., alpha, beta-unsaturated carbonyl compounds; and/or
c) the ability to perform steps a) and b) in a one-pot process.
The primary catalyst can be selected from homogeneous or heterogeneous, organic, inorganic or complex metal compounds including oxides, hydroxides, carbonates, carboxylates, acetylacetonates among others.
The activator/modifier can be selected from a wide array of phenolic compounds including phenol, hydroxyphenols, mono- and poly-substituted alkyl phenols, alkoxyphenols, aminophenols, nitrophenols, hydroxyacetophenones, salicylic acid and its derivatives, para-hydroxybenzoic acid and its derivatives, among others.
In one embodiment, the present invention can be employed in the manufacture of high quality fragrance and flavor grade products such as isomers of carveol and carvone.